This invention relates to a wheel bearing assembly for supporting a driven wheel of an automobile.
FIG. 7 shows a conventional wheel bearing assembly of this type. This bearing assembly comprises a homokinetic joint having an outer ring 30, a hub 32 integrally formed on the outer end of the outer ring 30 and having a flange 31 for supporting a driven wheel, and a bearing outer ring 34 mounted around the outer ring 30 through a plurality of rows of balls 33 and secured to the vehicle body.
When assembling this bearing assembly, the bearing outer ring 34 is slid onto the hub-carrying outer ring 30 from its end. This means that the inner diameter of the bearing outer ring 34 has to be larger than the outer diameter of the outer ring 30.
Thus, conventional bearing assemblies of this type were all very large and heavy. It is not desirable to mount such a large and heavy assembly on an automobile, which is required to be as lightweight as possible.
Also, the outer ring 30 has to have a sufficiently large outer diameter at its portion supporting the bearing outer ring 34, so that it tends to be rather heavy. Such a heavy outer ring 30 tends to produce such a large inertia moment while the vehicle wheels are rotating that the steerability of the vehicle deteriorates markedly.
Unexamined Japanese Patent Publication 63-106426 proposes a solution to this problem. As shown in FIG. 8, the wheel bearing assembly disclosed in this publication has a hub 41 having its end butted and welded at 44 to one end of the outer ring 40 of the joint. Around the hub 41, a bearing outer ring 43 is supported through balls 42 arranged in two rows.
When assembling this bearing assembly, the bearing outer ring 43 is fitted on-the hub 41 before joining the hub to the outer ring 40 of the joint. This arrangement makes it possible to reduce the diameters of the bearing outer ring and the hub. It is thus possible to reduce the size and weight of the entire wheel bearing assembly.
But the wheel bearing assembly shown in FIG. 8 has one problem. Namely, when torque is transmitted between the outer ring 40 of the joint and the hub 41, an extremely large load acts on the weld portion 44. Thus, the weld portion 44 has to be strong enough to withstand such a large load. In order to weld the hub to the outer ring of the joint with sufficient strength, they have to be welded together over their entire contact surface by friction welding or by any other welding method which tends to heat the joint surface to extremely high temperatures. If the joint surface is heated excessively, the outer ring 40, hub 41, balls 42 and bearing outer ring 43 will also be heated excessively, to such an extent that they are annealed. As a result, their hardness and strength drops markedly. Also, by being heated, their dimensions may change due to thermal strain.
It is usually necessary to pressurize the balls 42 of such a wheel bearing assembly to keep the bearing portion rattle-free. The wheel bearing assembly shown in FIG. 8 has a problem in this regard, too, because it is impossible to apply a predetermined pressure to the balls 42 with high precision.
A wheel bearing assembly described in Unexamined Japanese Utility Model Publication 3-75003 has a hub fitted on and joined by bolts or nuts to a shaft portion of the outer ring of the joint. When tightening the bolts or nuts, the balls are pre-loaded because the hub and the outer ring are moved axially relative to each other.
But the bolts or nuts may loosen due to vibration while in use. Thus, the outer ring and the hub cannot be joined together reliably.
An object of this invention is to provide a small, compact wheel bearing assembly which can be assembled easily while keeping a high reliability of the connection between the joint outer ring and the hub.